5580 J. Agric. Food Chem., Vol. 56, No. 14, 2008
Siskos et al.
a concentration of 5 µg/cm2 (Table 1.I). When 5 µg/cm2 of
F226 was tested, the same insect mortality was attained.
However, when F226 was tested at concentrations equivalent
to that of its natural presence in fraction F22, a lesser degree
in insect mortality was achieved (Table 1.II). 6′,7′-Epoxy-
bergamottin (fraction F226) exhibited substantial toxicity when
tested individually, while the other major components, osthol
in fraction F222 and bergapten in F224, were inactive. This is
the first report of the insecticidal activity of 6′,7′-epoxyber-
gamottin. However, 6′,7′-epoxybergamottin has been reported
to inhibit the activity of the enzyme cytochrome P450 3A4
(CYP3A4) (19, 20). Comparison of the insecticidal activity
of 6′,7′-epoxybergamottin and its precursor, bergamottin,
revealed that the epoxide group is essential for the insecticidal
properties of 6′,7′-epoxybergamottin, since bergamottin was
inactive even at high concentrations (data not shown).
Although bergamottin did not show any significant effect on
the olive fruit flies when tested individually in the Petri dish
exposure bioassay, it has been reported to exert antifeedant
activity to several species of Lepidoptera (21, 22). The
coumarin osthol when tested alone did not exhibit any activity
on B. oleae flies. However, osthol is known as an antibacte-
rial, antimalarial, antimutagenic, cytostatic, and cytotoxic
agent (23, 24). Also the antifeedant activity of bergapten is
well-documented (21, 22, 25)
Mixing of the three components (osthol, bergapten and 6′,7′-
epoxybergamottin) increases the adults’ mortality to the level of
the initial fraction (F22), indicating the occurrence of a synergistic
effect (Table 1.II). Furanocoumarins have been reported to elicit
behavioral responses and physiological effects in herbivorous
insects. They are repellents and feeding deterrents (5) as well as
toxins (26). In addition to their inherent toxicity, they may act
synergistically (21) or antagonistically (27) when mixed with other
coumarins or furanocoumarins. Toxicity in most instances is greatly
enhanced in the presence of UV light, suggesting that photoacti-
vation, possibly involving DNA, is a major mechanism of toxicity
(28). However, there are also toxic effects of furanocoumarins,
presently known, that are independent of UV light (26).
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Considering the advantages of using botanical insecticides
for pest management, it can be concluded that C. aurantium
peel extracts could have great potential for the control of
insect pests, particularly taking into account the effect of
synergism present in this case. It is well-established that the
evolution of insect resistance to plant extracts is extremely
slow, in contrast to resistance to pure compounds, which
develops rapidly (29).
ACKNOWLEDGMENT
We gratefully acknowledge Dr. David Kelly (Department of
Chemistry, Cardiff University) for his help on the 1H NMR
analyses. We also thank Dr. M. Berenbaum (Department of
Entomology, University of Illinois) for providing authentic osthol
samples.
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analysis. Trans. N. Y. Acad. Sci. Ser. 2 1953, 16, 88–97.
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S.; Kiuchi, F.; Yamazoe, Y.; Tsukamoto, S. Paradisin C: A new
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